The aim of this proposal is to characterize the cellular and extracellular composition of the dental follicles and bony crypts of the rat mandibular molars before and during tooth eruption. In non-continuously erupting dentition such as seen in the dog, the dental follicle is necessary for tooth eruption. In the dog, prior to eruption there is an influx of monocytes into the coronal region of the follicle and cytological evidence then suggests that these monocytes migrate to the bony crypt where they fuse to become osteoclasts for resorption of alveolar bone. The rat mandibular molars also exhibit non-continuously erupting dentition but little is known about the composition of their dental follicles before and during tooth eruption, as well as any changes which may occur in the bony crypts. Thus, this proposed study will utilize light and electron microscopy to determine the morphology of the dental follicles and bony crypts of the rat mandibular molars before and during eruption. If any unusual cell types such as monocytes are seen to increase or decrease in number at a given time, their numbers will be quantitated. Moreover, this study will not only characterize the cellular events that may occur in the dental follicles and bony crypts of the rat molars but also will determine if they correspond to the cellular changes that occur in the non- continuously erupting dentition of the dog. If they do, then many experiments that are not feasible with dogs because of their cost and size could be done with rats. The data obtained from this study also eventually will have clinical applications for controlling tooth eruption and tooth loss in humans. For example, clues as to how to facilitate eruption of impacted teeth or prevent loss of deciduous teeth without permanent successors may come from this study. Equally important, information obtained about bone resorption in the bony crypts during tooth eruption may lead to an understanding of how to prevent alveolar bone loss in periodontal disease.